1. Field of the Invention
The present invention relates to a scanning optical system, an optical scanning device, and an image forming apparatus.
2. Description of the Related Art
Optical scanning device are widely known in connection with a laser printer and digital copiers. A scanning optical system is used for the optical scanning device and an optical system wherein the light flux deflected by an optical deflector is condensed on a scanned surface as an optical spot.
Conventionally, the number of lenses of the scanning optical system formed as a lens system varies from one to a plurality. Although a unitary lens is effective for reducing manufacturing costs, the number of design parameters of the scanning optical system formed by a unitary lens is extremely small as compared with the scanning optical system formed by a plurality of lenses. Hence, it is difficult to realize good aberration correction in a case of a simple lens surface configuration.
In addition, it has been suggested to better correct the aberration and a uniform velocity property of the scanning optical system formed by a unitary lens by applying a specific lens surface configuration, as shown in Japanese Laid-Open Patent Applications, No. 9-33850, No. 10-90620, and No. 10-148755.
In order to respond to recent demand that the optical scanning device have a high density of the optical scanning, it is required for the optical spot to have a small diameter and stability. In order to realize an optical spot with the small diameter and stability, it is important to make uniform the wave-optic wavefront aberration whatever the image height is, as well as to improve the geometric-optic aberration, for the scanning optical system. However, the above mentioned publications do not refer to such wave-optic wavefront aberration correction.